Combating weeds and algae with 2-chloro-5-aryl-1,3,4-thiadiazoles

ABSTRACT

5-ARYL-TETRAZOLES MAY BE REACHED WITH THIOPHOSGENE TO YIELD 2-CHLORO-5-ARYL-1,3,4-THIADIAZOLES WHICH HAVE UNUSUALLY SELECTIVE PHYTOTOXIC PROPERTIES, BEING PARTICULARLY USEFUL IN COMBATING CRABGRASS AND ALGAE.

United States Patent O "ce I 3,690,858 COMBATING WEEDS AND ALGAE WITHZ-CHLORO-S-ARYL-1,3,4-THIADIAZOLES Norman A. Dahle, Mission, Kama,assignor to Gulf Research & Development Company, Pittsburgh, Pa. NoDrawing. Filed Oct. 24, 1969, Ser. No. 869,329 Int. Cl. A0111 9/12 US.C]. 71-67 2 Claims ABSTRACT OF THE DISCLOSURE S-aryl-tetrazoles may bereacted with thiophosgene to yield Z-chloro-S-aryl-1,3,4-thiadiazoleswhich have unusually selective phytotoxic properties, being particularlyus ful in combating crabgrass and algae.

DESCRIPTION OF INVENTION It has been discovered that a relatively smallclass of compounds having the structural formula,

in which X, Y and Z are selected from the group consisting of hydrogen,chloro and methyl have unusually specific selective herbicidal action,particularly against crabgrass and algae, and may be made by a. methodwhich is both novel and convenient. The synthesis and use of thesecompounds is discussed below, with specific examples presented by way ofillustration.

SYNTHESIS PROCEDURE 5-aryl-tetrazoles The tetrazole starting materialused in this synthesis scheme was prepared by the method of W. G.Finnegan, R. A. Henry and R. Lofquist which utilizes the reaction of anarylnitrile with a mixture of ammonium chloride and sodium azide indimethyl formam-ide containing a catalytic amount of lithium chloride:

Finnegan, W. G., Henry, R. A2, and Lofquist, R., J. Am. Chem. Soc. 80,3908 (1958) and U.S. Pat. 2,977,372.

The following procedure'is representative of the novel method ofsynthesis of the 2-chloro-5-aryl-1,3,4-thiadiazoles.

2-chloro-5-phenyl-l,3,4-thiadiazole A stirred mixture of 74.4 g. (0.50mole) of 5-phenyl- ZH-tetrazole and 74.0 g. (0.65 mole) of thiophosgenein 550 ml. of dimethoxyethane was allowed to reflux overnight. Thereaction mixture was cooled and filtered. The filtrate was taken todryness at reduced pressure and the resulting residue leached with two220-m1. portions of hexane. Upon cooling and concentration of thecombined hexane portions 40.5 g. of the desired product was obtained:M.P. 82-84 (lit. 86-88).

3,690,858 Patented Sept. 12, 1972 Use of the2-ch1oro-5-ary1-1,3,4-thiadiazoles as herbicides So as to illustrateclearly the selective phytotoxic properties of the herbicides, a groupof controlled greenhouse experiments is described below.

(1) POST-EMERGENT USE) An aqueous dispersion of each active compound wasprepared by combining 0.4 gram of the compound with about 4 ml. of asolvent-emulsifier mixture (3 parts of a commercial polyoxyethylatedvegetable oil emulsifier, one part xylene, one part kerosene) and thenadding water, with stirring, to a final volume of 40 ml.

The species of plants on which each compound was to be tested wereplanted in four-inch pots in a greenhouse. Ten to eighteen days afteremergence of the plants, three pots were sprayed with an aqueousdispersion of the active compound prepared as described above, at a rateof 5 lb. of active compound per acre and at a spray volume of 60 gallonsper acre. Approximately one week after the spray application the plantswere observed and the results rated according to the following schedule:

Type of action: Degree C=chlorosis (bleaching) 0=no eifect. N=necrosisl=slight effect. G=growth inhibition 2=moderate effect. F :formative e ff e c t (abnormal form of growth) 3=severe effect. K=non-emergeuce4=maximurn eifect (all plants died).

The same rating schedule was employed to judge preemergent resultsobtained according to the procedure below.

(2) PRE-EMERGENT USE A solution of each active compound was prepared bydissolving 290 mg. of the compound to be tested in 200 ml. of acetone.Disposable paper trays about 2 inches deep and half the size of ordinarygreenhouse flats were prepared and seeded with a variety of species ofplant seeds, then sprayed with the acetone solution at the rate of 10lb. of active chemical per acre of sprayed area. One flat, which hadbeen seeded with alfalfa, brome, flax, oats, radishes and sugar beetswas held at F. day temperature; another seeded with corn, coxcomb,cotton, crabgrass, millet and soybeans was held at F. Twenty-one daysafter seeding and treatment the flats were examined and herbicidaleffect was rated according to the above schedule.

Both post-emergent and pre-emergent results are set forth in thefollowing table.

32 203 .833 5 A? 2 830 mo momwuommsm Q 0 48 Bo 035 2820 2 munmomaou o$20 25 o uosum Q Q 05 we S Q: @3 23 B Q QQ G 2 0 DE: Hz 4 w mm Q 5 Q Q E5 Q g Q a Q 2m Lmu 5 6 5 5 Q0 3 2 Y Q E E T E Q Hz Q2 Q2 :3 z z 0 OQTEMS mo w 90 Q Q Q Q Mm Q Q Q Q MW QM ..:...8m 5 5 5 5 E Q Q Hz Hz E Q Q QN Hz 72 AZ :5 .55 8 92 2 0 DQQTQS Hm 0 E 3 M2 M0 w 6 1 HO c H6 0 c TU QNU o HG #M 12.23% Q Q Q Q Q Q Q Q Q Q Q Q :3 2'2 o 021: m Q0 m E Q 3 Q QQ2 5 Q 8 Q g QM m 16 mm Mm Mm Mm Mm v E 2 Mm E M Wm M ism z z o DQQQQ #2Q 3 w 5 Q Q Q Q Mm Q Q Q 5 QM m 5 6 5 Q Q Q Q N E Q Q Q E n E 5 Hz Q m o05% 2 m w 5 Q Q Q Q Q Q Q 8 Q no QM m Q Q Q Q Q Q Q Q Q Q Q Q :8 2'2Q3809 H5593 32B 33 n wmm warm EQO Q30 23:4 QSQQO $3.3m QQEE 088m nBoQnomwEmnEO H32 .8 n wow EEG Ewan 2:5 R5355 All the compounds exhibitedalgicidal activity at 8.6 p.p.m. in aqueous media containing growingalgae. The following four compounds were also effective at 1 p.p.m.concentration.

2-chloro-5-phenyl-l,3,4-thiadiazole2-chloro-5-(3-methylpheny1)-1,3,4-thiadiazole 2chloro-5(2-chlorophenyl)-1,3,4-thiadiazole 2-chloro-5- (4-chl0rophenyl)1,3,4-thiadiazole These compounds are preferred for combating algae incooling water ponds, reservoirs, tanks and irrigation ditches becausethey may be used at concentrations so low as to be practically harmlessto plant and animal life.

I claim:

1. Combating crabgrass by applying preemergently to 15 the locus of thecrabgrass seeds an effective amount of a 2 chloro 5aryl-1,3,4-thiadiazole having the structural formula in which X, Y and Zare selected from the group consisting of hydrogen, chloro and methylsubstituents.

2. Combating algae by applying to the locus of the algae an effectiveamount of a compound having the generic structural formula ReferencesCited UNITED STATES PATENTS 20 3,522,267 6/1970 Duerr et al. 71-90 JAMESO. THOMAS, 111., Primary Examiner US. Cl. X.R.

